Fuel cells are a clean and efficient electric power source proposed for use in a variety of applications, including replacing or supplementing the internal combustion engines currently employed in automobiles. A fuel cell assembly comprises an anode (i.e., a negatively charged electrode where the oxidation reaction takes place), a cathode (i.e., a positively charged electrode where the reduction reaction takes place), and an electrolyte in between the two electrodes. In order to produce sufficient electric power for use as a vehicle engine, fuel cell engines typically employ a fuel cell stack comprising multiple fuel cell assemblies (e.g., about 100 or more fuel cells) connected in series. While a single fuel cell may operate at a DC voltage of about 0.6 volts to about 1.0 volts, an automotive fuel cell stack may operate at a DC voltage of 125 volts to 450 volts.
In fuel cell systems, the components of the individual fuel cell, for example, the anode, cathode, and/or bipolar plates, contain coolant channels. The coolant channels circulate a coolant about each fuel cell assembly within the fuel cell stack. In circulating a coolant through the coolant channels, the temperature of the fuel cell stack may be controlled by regulating the coolant flow and temperature.
The cooling system surrounding the fuel cell stack, however, is exposed to the same voltage as the fuel cell stack itself. To reduce the electrical shock possibility within the fuel cell stack, the coolant should have a low conductivity such as, for example, less than about 5 microseamens/cm (μS/cm). During normal operation of a fuel cell system, corrosion, leaching, and decomposition of coolant system parts may lead to the production of ionic species which can increase the conductivity of the coolant. To prevent the coolant from exceeding the conductivity limits, a mixed bed ion exchange resin filter may be employed to remove the ionic species which are produced. Because of the low conductivity requirements and the expected use of mixed bed ion exchange resins, the use of corrosion inhibitors may not be feasible with these systems. This is at least in part because many corrosion inhibitors comprise ionic species. At the concentration of the inhibitors employed to provide effective corrosion protection, the coolants containing the inhibitors may have a conductivity that is higher than the acceptable limits of less than about 5 μS/cm. In addition, these ionic corrosion inhibitors may be removed by mixed bed ion exchange resins.
There thus remains a need for compositions and methods to maintain coolant conductivity at desirable levels during the operation and lifetime of a fuel cell system, and/or to prevent corrosion of the fuel cell system during use.